Reference is first made to FIGS. 1-4. In FIG. 1, a standard definition (SD) television set 10 is illustrated having a format for displaying video images with an aspect ratio of 4:3. The “aspect ratio” is the proportion of the width of a video image with respect to its height. SD broadcast signals conform to the 4:3 format and can be displayed over the entire screen of the traditional SD television set 10. FIG. 2 illustrates a high-definition television (HDTV) set 20, which has an aspect ratio of 16:9 for displaying high-definition (HD) signals also having a 16:9 aspect ratio. With respect to cinematography, aspect ratios of 2.39:1 and 1.85:1 are common, but do not match the format of the SD television set 10.
Because of the difference in aspect ratios, the SD television set 10 is normally unable to display cinematic movies over the entire screen thereof. Also, the HDTV set 20 is normally unable to display SD video images over the entire screen of the HDTV set 20. When the aspect ratio of a display screen, such as the SD television set 10 or HDTV set 20, is different from the video image being displayed, certain adjustments are made so that the video images can be easily viewed. For example, a control device (not shown), which controls the video images to be displayed on the display screen, may crop a portion of video image so that the image covers the entire screen. Alternatively, the control device may fit the video image such that there will remain unused or blank spaces on the screen, which is the typical solution to accommodate differences in aspect ratios. In this typical solution, black bands are typically added in the unused spaces. In FIG. 3, the SD television set 10 of FIG. 1 displays a “wide-screen” video image 12, such as a cinematic movie, the width of which is bounded by the left and right sides of the screen of the SD television set 10. Blank spaces 14 and 16 are positioned above and below the video image 12 in a “letterbox” configuration. In FIG. 4, an SD video image 22 is displayed on the HDTV set 20 of FIG. 2. The height of the SD video image 22 is bounded by the top and bottom of the screen of the HDTV set 20 and blank spaces 24 and 26 are positioned to the left and right of the SD video image 22 in a “pillarbox” configuration.
Typically, these blank spaces 14, 16, 24, and 26 are simply configured as black bands filling the empty portions of the screen. However, there is a problem that can arise when the unused spaces are filled with black bands. Over extended periods of time, the portion of the display screen that includes the images 12 and 22 will experience a burn-in effect that is more severe than the unused black portions of the screen. The images 12 and 22 may imprint a burn pattern on the luminophor or phosphor material of the display screen 10 and 20. Since the black bars 14, 16, 24, and 26 create little or no burn-in effect on the unused portions of the screen, these portions will not be burned to such an extent, thereby resulting in an uneven burn pattern. With an uneven burn pattern, unnatural lines or bars might be created on the display screen that may be visible when later images are shown. Also, these unequal burn patterns can be permanently imprinted on a display screen and are undesirably distracting to viewers.
One solution to the problem of unequal burning on a display screen has been to color the unused spaces gray. In theory, by exposing the unused portions of the screen to a neutral color between the extremes of white or black, the gray blocks are intended to burn the unused portions of the screen to a similar extent as the burning where the actual video image is displayed. However, the gray color may appear unnatural compared to colorful images and may be distracting to a viewer. Also, the illumination of gray may not necessarily burn the unused portions equally with the regular image, thereby still creating the undesirable burn lines or bars. Thus, a need exists in the field of television to address the aforementioned deficiencies and inadequacies of the conventional systems for filling the unused spaces of a display screen.